Add pc/ — PyInstaller build scripts, .ico icon, and README

pc/README.md

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+# pc/ — Kanjin Windows Standalone
+
+Build a single `.exe` that players can double-click to play — no Python, no IDE, no dependencies.
+
+## Build it
+
+```batch
+cd pc
+build.bat
+```
+
+Deliver `pc\Kanjin.exe` (~35 MB). The player double-clicks it, a console window opens, the game starts.
+
+## What's inside
+
+| File | Purpose |
+|---|---|
+| `build.bat` | Windows batch script — runs PyInstaller with the right flags |
+| `build.sh` | Linux/macOS equivalent (for cross-builds) |
+| `kanjin.ico` | Application icon embedded in the .exe |
+| `generate_icon.py` | Creates `kanjin.ico` from a solid-colour PNG (run once) |
+
+## Requirements
+
+- Python 3.11+ installed on the **build** machine
+- `pip install pyinstaller` (installed automatically by build.bat)
+
+The **player's** machine needs nothing — the .exe is fully self-contained.